Browsing by Subject "Stratigraphy"

Now showing 1 - 8 of 8
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    Gafvert Lake Reconnaissance Mapping Project
    (University of Minnesota Duluth, 2005) Heine, John J
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    Geologic and Stratigraphic Controls of the Biwabik Iron Formation and the Aggregate Potential of the Mesabi Iron Range, Minnesota
    (University of Minnesota Duluth, 2009) Severson, Mark J; Heine, John J; Patelke, Marsha Meinders
    The taconite mines on the Mesabi Iron Range of northeastern Minnesota generate millions of tons of mined waste rock annually that could potentially be used as aggregate material in road building projects. Paramount to defining potential aggregate horizons within the mined ironformation is an understanding of the stratigraphy as it relates to mined ore units and waste units at each of the respective taconite mines. However, each mine uses a different submember terminology to designate the various ore and waste horizons. The major emphasis of this investigation was to produce a stratigraphic “Rosetta Stone” of the Biwabik Iron Formation that ties the stratigraphy and differing submember terminology of one mine to all of the other mines on the Mesabi Iron Range. Toward that end, the Natural Resources Research Institute (NRRI) looked at core from over 380 drill holes, and some mine exposures, in the central and western Mesabi Iron Range (Biwabik to Coleraine, MN area) to develop a stratigraphic system that links all of the mined ore and waste submembers. The methodology used in this investigation was to log multitudinous deep drill holes from a single mine, hang all of the drill holes on a common datum (bottom of the Lower Slaty member), and then correlate all of the submembers, as used by that particular mine, making note of bedding features and other unique features that define a particular submember. This same system of “logging, hanging, and correlating” was done at each of the taconite mines (seven different mines/areas along the Mesabi Iron Range) to better understand each mine’s submember terminology. The hung stratigraphic-sections from each mine were then used to collectively make generalized stratigraphic columns for each of the mines. These stratigraphic columns were then added to the “Rosetta Stone” (Plate II of this report) that is used to illustrate how the submembers at one mine correlate with similar submembers at all of the other mines. In the end, this investigation identified 25 major “Rosetta” units that define the stratigraphy of the Biwabik Iron Formation that can be used to link together all of the differing submember nomenclatures from the various taconite mines. This division of the iron-formation into 25 major units, based primarily on their overall bedding characteristics, is applicable to only the central and western Mesabi Iron Range and does not include the more highly metamorphosed iron-formation of the eastern Mesabi Iron Range, e.g., to the east of Aurora, MN.
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    Geology and SEDEX Potential of Early Proterozoic Rocks, East-Central Minnesota
    (University of Minnesota Duluth, 2003) Severson, Mark J; Zanko, Lawrence M; Hauck, Steven A; Oreskovich, Julie A
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    OFR16-01, Quaternary stratigraphy of Minnesota: statewide cross-sections, Minnesota Geological Survey
    (Minnesota Geological Survey, 2016) Lusardi, B.A.; Gowan, A.S.; Meyer, G.N.; Thorleifson, L.H.
    Seven cross sections were constructed as part of our comprehensive plan to formally define and map Quaternary lithostratigraphic units across Minnesota.
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    Probabilistic, Rule-Based Modeling of Deltaic Networks and Stratigraphy
    (2021-09) Cazanacli, Dan
    This research is centered on developing simplified models that can reproduce natural deltaic distributary networks and deltaic stratigraphy at channel scale resolution. Modeling distributary channel networks poses unique challenges due to the complexity and limited understanding of the main genetic processes responsible for channel branching and network evolution. We explore to what extent a model based on a minimal set of rules can replicate channel arrangements that are representative of field deltas. The proposed model is based on a partly correlated random walk algorithm for generating individual branches coupled with a bifurcation probability that translates into channel branching generating networks. Systematic and heuristic exploration of the input indicates that if the probability distributions and the proportions between terms are properly constrained the model can predictably generate realistically looking networks that, by several metrics (reach lengths distribution, relative location of bifurcation nodes, dispersion of the outlets, and overall delta shape) are comparable to a number of natural distributary networks. To model deltaic stratigraphy a novel approach based stochastic superposition of deltaic networks is introduced as an alternative approach to forward process modeling. Stratigraphic sequences are realized through guided (i.e., rule based) superposition of topographic surfaces sampled from a large (104) database of distributary networks that are topologically similar to field deltas. The approach is well suited for subaerial deltas which are characterized by stochastic processes that are difficult to implement numerically (i.e., avulsion, bifurcation, and channel migration).
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    Time, Life and Environment: Practices of Geohistory at the Intersection of the Earth and Life Sciences
    (2021-07) Dresow, Max
    In his great work on fossil bones (1812), Georges Cuvier compared our ignorance of geohistory to our conceptual mastery of the heavens. Several centuries of research had “burst the limits of space” and drawn back the curtain on the hidden mechanism of the universe. Yet deep time remained obscure, shielded from inquiring eyes by the inconvenient fact that the past no longer exists. To “burst the limits of time,” scientists needed to overcome this barrier—needed, in other words, to extend their epistemic reach into the deepest stretches of geohistory. This dissertation is framed by this grand epistemological challenge. How do scientists “burst the limits of time” in order to unravel the complicated thread of time, life and environment? Cuvier was among the first people to show how the vanished contents of deep time might be reconstructed from surviving material evidence. Yet his achievement did not solve the epistemological problem once and for all. Over the past two hundred years, scientists have burst the limits of time again and again—new barriers, new ruptures. It is this process that interests me. I am particularly interested in how scientists from multiple disciplines pool their conceptual and material resources to reconstruct different aspects of complex historical events. In addition, I am interested in the strategies researchers have developed to probe the interactions between living things and their environments on a range of spatial and temporal scales. The dissertation is organized into five chapters of unequal length. After a brief Preface, Chapter 1 situates the project in three overlapping bodies of literature. These are: (1) philosophical studies of the “historical sciences,” (2) philosophical discussions of paleontology, and (3) philosophical discussions of scientific practice associated with the “practice-turn.” This exercise enables me to articulate my aims for the project, and (no less important) to say what this dissertation is not about. The remainder of the chapters concern historical and philosophical topics in the sciences of geohistory. Chapter 2 examines a “start-up problem” in nineteenth century geology: how were fossils turned into a reliable yardstick for measuring geological time? I argue that in order to use fossils to measure time, geologists had to overcome a “problem of nomic measurement” (so named by Hasok Chang). Moreover, and contrary to philosophical expectations, they did not do this by formulating a theoretical explanation of the operative phenomena. Instead they pursued a more piecemeal strategy guided by practices of heuristic appraisal—something I suggest is typical of justification in start-up situations. In Chapter 3, I turn to the subject of explanation, and explore why explanations of complex historical events tend to grow more complicated over time. Using inquiry into earth’s largest mass extinction as an illustration, I argue that the main driver of explanation in geohistory is “non-explanatory work”: work that may be relevant to the evaluation of explanatory hypotheses, but that is not undertaken in the interest of testing an explanatory claim. This “drives” explanation by bringing new features of historical phenomena into focus—and this in turn creates new demands (adequacy conditions) on explanations, prompting investigators to develop more complex explanatory models. In Chapter 4, I explore the concept of “uniformitarianism”: perhaps the most contentious term in the geological literature. Since this is a polyvalent term, many commentators have assumed that its controversial status arises from a sort of semantic chaos, which sows confusion among otherwise competent language users. However, I argue that debates about uniformitarianism in geology do not arise from a mere babel of meanings. Instead, they arise from legitimate disagreements about substantive questions, for example, “Is uniformitarianism necessary?” and “When is it appropriate to offer non-uniformitarian explanations of past events?” This chapter examines these questions, and relates them to several “forms of understanding” pursued by researchers in geohistory. Finally, in Chapter 5, I explore the emergence of a new approach to stratigraphic complexity, first in stratigraphy, and then, following its creative appropriation, in paleobiology. The approach is based on pioneering models of sedimentary basin filling, and has come to be associated with an approach known as “stratigraphic paleobiology.” This chapter traces the emergence of stratigraphic paleobiology and explores how it reconfigured the cultural landscape of paleobiology following the Paleobiological Revolution. It also considers how the new stratigraphy is shaping paleontological discussion of “incompleteness” and “bias” in the fossil record.
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    Topography, image, and flow model data for experimental density currents, St. Anthony Falls Laboratory, 2015-2017
    (2018-01-08) Limaye, A. B.; Grimaud, J.-L.; Lai, S. Y. J.; Foreman, B. Z.; Komatsu, Y.; Paola, C.; aslimaye@umn.edu; Limaye, A. B.
    Submarine channels convey turbidity currents, the primary means for distributing sand and coarser sediments to the deep ocean. In some cases, submarine channels have been shown to braid, similarly to rivers. Yet the strength of the analogy between the subaerial and submarine braided channels is incompletely understood. This data set includes topography, image, and flow model data for six experiments with subaqueous density currents and two experiments with subaerial rivers. The experiments were conducted to quantify (1) submarine channel kinematics, and (2) the responses of channel and bar geometry to subaerial versus submarine basin conditions, inlet conditions, and the ratio of flow-to-sediment discharge (Qw/Qs).The data set accompanies a 2018 publication in the journal Sedimentology.